Many irrigation districts have made the switch to a more environmentally friendly aquatic herbicide and plan to stick with it despite a steep learning curve.

Endothall, an aquatic herbicide that includes Cascade and Teton, allows irrigation districts to control moss and other aquatic weeds without killing fish and other aquatic life.

But endothall doesn't act as quickly as some of the other aquatic herbicides that irrigation districts have used in the past. Districts plan to make some adjustments this year in hopes of staying ahead of the weeds.

"Our plan is to apply at a little heavier rate and get started a little earlier," said Brian Olmstead, general manager of the Twin Falls Canal Co. in south-central Idaho.

Endothall has been used for years in lakes and ponds, but wasn't granted full registration for use in canals and ditches until 2010. The Environmental Protection Agency granted the registration just before the irrigation season last year.

The Twin Falls Canal Co. conducted its first full-scale application of endothall in 2009 under a special emergency exemption.

Irrigation managers say they're confident that endothall will prove to be an effective and economical tool as they gain more experience with it.

Canal companies in south-central Idaho have always had to exercise extreme caution when treating canals and ditches because of nearby fish hatcheries and fish farms.

Endothall represents "a revolutionary breakthrough," because it doesn't harm fish, frogs, snails and other aquatic life and is safer for workers to handle, Olmstead said.

"The potential for lawsuits was extreme with the other products," he said.

The switch to endothall helped the North Side Canal Co. reduce its weed control expenses by about $200,000 last year, water quality specialist Larry Pennington said.

One application of Cascade can treat up to 50 miles of canal.

The company applied the chemical once at seven sites last year. Under the old herbicide system, the company treated 90 different sites with up to seven applications.